Many conventional recording apparatuses, such as copiers or laser printers, use an aluminum substrate for a photosensitive drum. An exposure process commonly exposes the surface of a photosensitive layer on a substrate in these recording apparatuses. Since conventional methods for obtaining a photosensitive body require devices for charging, exposure, development, transfer, fixing, electrostatic elimination, and cleaning processes to be located around the photosensitive drum, it is difficult to miniaturize the recording apparatus. As a result, a developer may splash from a developing machine, contaminating optics for an exposure apparatus and adversely affecting printing.
To solve this problem, an internally illuminating apparatus of a reduced size has been devised, which prevents the optics from being contaminated by the splashing developer by using a photosensitive drum formed by applying a conductive layer and a photosensitive layer to a transparent substrate; installing a light source for an exposure apparatus inside a photosensitive body; and irradiating the photosensitive body with light from the inside. Existing methods for a photosensitive drum used for such an internally illuminating electrophotographic apparatus form a film of indium tin oxide (hereinafter referred as "ITO") by means of sputtering or vacuum evaporation in order to form a transparent conductive layer on inorganic glass that is a transparent substrate. In addition, Japanese Patent Application Laid Open No. 7-319195 (applicant: FUJITSU Ltd.) describes a photosensitive drum in which doped polyaniline is laminated on a cylindrical glass substrate.
The use of a photosensitive drum for an internally illuminating electrophotographic apparatus has the following problems. The cylindrical inorganic glass substrate is expensive and is susceptible to cracking, and its dimensional accuracy is low; when a transparent conductive layer is formed by means of sputtering or vacuum evaporation, the uniformity of the film thickness and the productivity are low; and the process for forming a doped polyaniline layer is extremely costly.
In view of the prior art manufacturing techniques, there is a need for a supporting substrate for an internally illuminating electrophotographic apparatus in which the material is inexpensive, its dimensional accuracy is excellent, its mechanical strength is sufficient to allow it to be used as a photosensitive drum, it has sufficient chemical stability to maintain its quality as a photosensitive drum even in a general atmosphere that is not particularly controlled, it has sufficient transparency to allow irradiation light to be transmitted therethrough during exposure without being refracted therefrom, it adheres well to a transparent conductive layer laminated thereon, and it has the solvent resistance and heat resistance required during the formation of a photosensitive layer that uses an immersion application process that has a high productivity.